Optical links are finding increased use across a number of application spaces, including, for example, chip-chip, board-board, data center/rack-rack, in wide area network (WAN) fiber-optic links, and the like. All of these links and networks are experiencing rapidly increasing growth of capacity. WAN capacity growth is reflected by individual channel data rate scaling from 10 Gbps, to 40 Gbps, to currently deployed 100 Gbps, and to future projections of 1000 Gbps channels. The same capacity growth demand is also observed for shorter interconnects, as demonstrated by active optical cables which currently have >100 Gb of capacity (4×25 G, 10×10 G, etc.), and are starting to scale to 400 Gb capacity (16×25 G, 20×20 G, 40×10 G, etc.). Here, the ever-growing demand for increased bandwidth and channel capacity is being successfully met by Wavelength Division Multiplexing (WDM) evolving into a form of optical bound channels. Channels bound together include a set of optical WDM carriers generated and combined within the same optical module to create a composite line side signal whose capacity can be combined into a higher-data-rate aggregate channel of desired high capacity, and which is brought into service in one operational cycle. Bound channels provide efficient bandwidth scalability and higher composite data rates through extensive channel parallelization, similar to an approach used in multi-core microprocessors. At present, bound channels are utilized in interconnect scenarios at 100 Gbps and above.
Conventional direct-detect WDM optical channels as constituents of an optical bound channel have severe drawbacks. They are power and real estate wasteful due to massive parallel implementation of essentially redundant digital clock and data recovery (CDR) circuitry in every one of the individual channel receiver. Similar power and real estate concerns arise regarding the analog opto-electronic front end of the receivers, which typically uses a transimpedance amplifier (TIA). TIAs also require a high gain-bandwidth product, which has to increase as square of the signal bandwidth growth, and hits so called “transimpedance limit,” Eduard Säckinger, “The Transimpedance Limit,” IEEE Transactions on Circuits and Systems—I: Regular Papers, vol. 57, no. 8, August 2010, severely complicating process of further receiver bandwidth expansion. In view of imminent integration of photonic optical circuits and associated electronics, the power dissipation and real estate requirements for implementation of optical bound channels become of ultimate importance and cannot be easily satisfied within the architectural solutions inherent to conventional implementation of direct-detect WDM optical channels.